Polyurethanes that are curable by exposure to electron beams are usually prepared by end capping and isocyanate group of the desired polyurethane prepolymer with hydroxy-containing acrylate and methacrylate monomers. However, pendant, unsaturated groups cannot be inserted into the polymer chain using this approach.
Glyceryl allyl ether is a commercially available unsaturated diol which is used to insert unsaturated groups randomly into a polyurethane chain. However, the reactivity of the allyl group is less than desirable and the curing of the resulting polyurethane polymer is often sluggish. No other diols with more active functional groups such as acrylate, methacrylate or vinyl diols have been disclosed. There is a clear need for a means of inserting more active unsaturated groups randomly and at any desired level into urethane polymers. Such polymers could be more readily cured by high-energy e-beam radiation or with conventional free-radical initiators than those which include less active randomly inserted groups from glyceryl allyl ether.
U.S. Pat. No. 4,320,221 discloses a method for making curable adhesive compositions wherein the uncured composition comprises monomers or macromers, end capped with unsaturated methacrylate groups. In particular, this patent discloses the reaction of an isocyanatoethyl acrylate, particularly 2-isocyanatoethyl methacrylate with a polyahl such as diethanolamine in the presence of dibutyl-tin-dilaurate at temperatures of 70.degree. C. and above to form the monomers or macromers which are end capped with unsaturated methacrylate functional groups. Under the conditions of the reaction, all --OH, .dbd.NH or NH.sub.2 groups are reacted with the isocyanatoethyl methacrylate to form unsaturated methacrylate end capped monomers. Such monomers are useful as adhesives, but are not useful for inserting unsaturated groups ran-domly and at any desired level into polymer chains, particularly polyurethane polymers.